A PhD won't make you smart, but does make you read the literature. You could do that on the job, but who would? ...and who would pay you to? Real world experience won't give you even the breadth of knowledge (unless you're working with all the world-leading experts) - let alone feeling the value of the literature, and the skills to access it. This helps you avoid well-known stupid mistakes, and concentrate your energies on all-new stupid mistakes.

OTOH not knowing it won't work can help \_(ツ)_/